Cell phone use while driving is prevalent among young drivers. The risk of crashing is 4 times higher for drivers talking on the phone, and 23 times higher for those texting. Drivers aged 18-20 years have both the highest phone use while driving and the highest crash rate per capita among all ages. Unfortunately, educational efforts and legislative bans have not been effective in reducing phone use while driving, highlighting the need to explore other interventions. While technological solutions, including phone apps, may offer promising alternatives, research remains sparse. Specifically, there are to date no studies of the use of phone apps or other technological interventions to reduce phone use by high-risk young adults while driving. Therefore, we propose an R21 project with objectives to pilot test the feasibility and preliminary efficacy of a phone app for reducing phone use and high-risk driving events in drivers aged 18-20 years. We hypothesize that it is feasible to implement a cell phone app intervention among West Virginia University drivers. We also hypothesize that the cell phone use and high-risk driving events can be substantially reduced, if a phone app which limits cell phone use is active, and young drivers comply with it. The aims of this project are to test the feasibility of a cell phone app intervention on acceptance and retention, and identify facilitators and barriers for compliance (Aim 1), and to determine whether a phone app intervention reduces calling, texting, and high-risk driving events among drivers aged 18-20 years (Aim 2). A prospective, randomized, parallel-group, exploratory, three-arm trial will be conducted. Sixty students at West Virginia University will be randomized to receive: (1) a TXTL8R app with passenger override mode that blocks phone use while driving, but allows the use of the phone after pressing the passenger button; (2) a TXTL8R app without passenger override mode that blocks cell phone use when the phone is moving above a threshold speed; or (3) a sham app that allows and tracks calls and texts while driving. Participants will be studie for six months. The app will be set active in blocking phone use for four months, and inactive for the remaining two months for the intervention arms. The outcomes will include: (1) calling while driving; (2) texting while driving; (3) high-risk driving events as measured by an event-triggered accelerometer. We will conduct process evaluation and estimate preliminary efficacy of cell phone app in reducing calling, texting, and high-risk driving events. Guided by preliminary data, this study is also innovative. For example, we focus on an innovative technological approach for addressing the epidemic of driver phone use. We will employ novel video capture methods to identify high-risk driving events and assess the contribution of phone use to high-risk driving events. This study is significant, because the findings will provide preliminary data for a larger scale trial (R01 project) to investigate more definitively the efficacy of a phone app for reducing cell phone use, high-risk driving behaviors, and crashes in young adults.